A manual transmission of this kind comprises an internal combustion power transmission branch and an electromotive power transmission branch, which are brought together at the output shaft. The internal combustion power transmission branch comprises the first input shaft, the gear sets of the first group as well as the output shaft and allows the transmission of torque between the internal combustion engine, and the drive wheels of the motor vehicle drivingly connected with the output shaft. The electromotive power transmission branch comprises the second input shaft, the gear sets of the second group as well as the output shaft and allows the transmission of torque between the electric machine and the drive wheels of the motor vehicle. When the coupling device is disengaged, a purely internal combustion drive operation is thereby possible by means of a engaged gear set of the first group, a purely electromotive drive operation is possible by means of an engaged gear set of the second group, and a combined drive operation of both aggregates (internal combustion engine and electric machine) with operation of the electric machine as a motor or generator and with a fixed transmission ratio is possible by means of an engaged gear set of the first and second group respectively.
When the motor vehicle is at a standstill, the internal combustion engine can be started by means of the electric machine by engaging the coupling device. In addition, the gear sets of the second group are made available for the internal combustion drive operation and the gear sets of the first group are made available for the electromotive drive operation by engaging the coupling device. With an appropriate transmission ratio and allocation of the gear sets, fewer gear sets are needed overall and accordingly, the manual transmission can have a simpler and more compact design.
DE 199 60 621 B4 describes a manual transmission of this kind in three alternative designs. In all embodiments, the internal combustion power transmission branch has a first countershaft, which can be drivingly connected with the drive shaft of an internal combustion engine on the input side by means of a input constant, a first input shaft and a friction clutch, and can be drivingly connected on the output side with an output shaft by means of a first group of selectively shiftable gearwheel sets. In the first embodiment according to FIG. 1 there, a second input shaft is designed as a second countershaft, which can be connected in a rotationally fixed manner with the rotor of an electric machine and drivingly connected with the output shaft by means of a second group of selectively shiftable gearwheel sets. In this case, the coupling device comprises a drive stage disposed between the input shaft and the second countershaft as well as a shiftable clutch, which is disposed between the driving wheel of the drive stage on the countershaft side and the second countershaft.
In the second and third embodiment according to the FIGS. 2 and 3 there, the second input shaft is formed as a hollow rotor shaft, which is disposed coaxially over the input shaft and connected in a rotationally fixed manner with the rotor of an electric machine disposed coaxially over the first input shaft. The rotor shaft is drivingly connected with the second countershaft by means of a second input constant, which can be drivingly connected with the output shaft by means of the second group of selectively shiftable gearwheel sets. In this case, the coupling device comprises a shiftable clutch, which is disposed between the first input shaft and the rotor shaft.
In a further manual transmission of this kind according to WO 2008/138 387 A1, both input shafts are formed as countershafts. The first input or countershaft of the internal combustion power transmission branch can be connected with the drive shaft of an internal combustion engine on the input side by means of a controllable separator clutch and can be drivingly connected with an output shaft on the output side by means of a first group of selectively shiftable gearwheel sets. The second input or countershaft of the electromotive power transmission branch is connected with the rotor of an electric machine on the input side in a rotationally fixed manner and can be drivingly connected on the output side with the output shaft by means of a second group of selectively shiftable gearwheel sets. The gear sets of both groups are disposed in common radial planes and each use a common power take-off gear disposed on the output shaft. In this case, the coupling device is designed in such a way that the idler gears and the allocated gear clutches of two axially adjacent gear sets of the second group on the output shaft, which are combined into a shift set, are disposed on the output shaft, whereby it is possible to couple both input shafts independently of the shifting of one of the respective gear sets.
The known manual transmissions that are designed specifically for use in a hybrid drive of a motor vehicle are therefore relatively complex and expensive to manufacture. The market success of hybrid-powered vehicles, however, depends largely on favorable manufacturing costs of the components of the hybrid power train, and in particular of the manual transmission.